Aircraft: B737
Phase of flight: Initial Approach
Anomaly: Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Wake Vortex Encounter

After configuring for a flaps 30 landing on my hand flown; visual approach to Runway 22L at BOS; we experienced what I believe was a strong gust. This occurred just inside the final approach fix. The indicated airspeed rapidly increased and exceeded the flaps 30 placard speed of 175 kts. (The approach report from ACARS; retrieved upon arrival at the gate; indicated we reached 176 kts). The flap load relief system activated and automatically retracted the flaps to 25. This is the first time I've experienced this aspect of the flap protection system and my first reaction was that I'd failed to properly configure the flaps. The First Officer was quick to analyze what had just happened and when we had slowed sufficiently; we were able to reset the flaps to 30. The final flap setting; however; occurred just below 1;000 ft. The First Officer stated that we were not stable and I initiated a go-around. The First Officer backed me up on ensuring all the steps for the go-around were conducted in the proper sequence. We notified Tower and we were vectored around for another visual approach and landed without incident. The First Officer and I discussed the experience when we got to the gate. Though we don't like to do go-arounds; we were both satisfied that we did the right thing. I wrote up the flap over-speed in the AML and spoke with maintenance. A contributing factor may have been a very light landing weight; approximately 121;000 lbs. I can't praise the First Officer's situational awareness and professionalism enough. He made sure that all procedures were followed correctly and that all checklists were completed. As for me; I'll need to be more vigilant about airspeed control. I'll also reinforce the necessity to be prepared for a go-around on every approach--not just talk about it. Visual 22L BOS at approximately 1;300 ft. AFL; autopilot off; we encountered an abrupt pocket that altered the pitch of the aircraft; possibly a wake from the preceding A321. As PM I noticed an increase in speed and initially noted 175 kts. (flap 30 limit is 175 kts). My attention was drawn to the airspeed and ensuring the proper attitude and path were maintained. The PF called for flaps 30 which had been previously set and confirmed leading me to believe we had exceeded 176 kts causing the flap load relief. (The Before Landing Checklist had been completed and flaps 30 had been confirmed set.) The flap handle was again verified set to 30. Aircraft was slowed and flaps returned to 30 passing 1;000 ft. AFL. Due to the flap movement and airspeed the approach was not stable and a go-around was performed. The flap report indicated that an overspeed of 176 kts. occurred. Maintenance was informed verbally and with an appropriate AML entry.The decision to execute the Go-Around stems from the culture and training that stress the importance of stabilized approaches. B737-800 flight crew reported executing a go-around from their approach to BOS after a wind gust or wake encounter caused a momentary overspeed.